Electro-hydraulic servomechanism

ABSTRACT

A control valve including an electrical actuator and a two-stage hydraulic regulator. The regulator defines a closed-loop control where delivery of pressurized fluid to a load is managed and the regulator and actuator are isolated from one another except for a single fluid tight mechanical linkage.

United States Patent 11 1 1111 3,709,257 Faisandier 14 1 Jan. 9, 1973 [54] ELECTRO-HYDRAULIC [56] References Cited SERVOMECHANISM UNITED STATES PATENTS 175] Jwlues Faisandie" chatmmsws' 2 763 988 9/1956 Newell ..9l/46l x- Bagneux) France 2,977,984 4/1961 Barnes ...137/625.64 2,996,045 8/1961 Burton ....137/625.64 X [73] Assgnee' 5mm D Applicam' Des Mafhim 3,000,363 9/1961 Hayner et al ..l37/625.64 Molrices, Y Les Momma", 3,060,969 10/1962 Asian ..l37/625.63 France 3,395,617 8/1968 Kaptur ....137/625.64'X 3,230,841 1/1966 York ....137/625.66 X [22] Sept 1970 3,318,331 5/1967 Town .137/62563 21 Appl. No.: 74,776

Primary Examiner-Henry T. Klinksiek Assistant Examiner-Robert J. Miller 1 Fm'elgn pp Priority Data Attorney-Fshman and Van Kirk 57 ABSTRACT [52] U.S. Cl. ..l37/625.64 A control valve including an electrical actuator and a [51] Int. Cl ..F16k 11/00 two-stage hydraulic regulator. The regulator defines a [58] Field of Search ..l37/625.64, 625.6, 596.l6, closed-loop control where delivery of pressurized fluid to a load is managed and the regulator and actuator are isolated from one another except for a single fluid tight mechanical linkage.

10 Claims, 2 Drawing Figures ELECTRO-HYDRAULIC SERVOMECHANISM BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to servomechanisms. More specifically, the present invention is directed to electrohydraulic servomechanisms and particularly to electrohydraulic servo valves of the two stage type. Accordingly, the general objects of the present invention are to provide novel and improved apparatus of such character.

2. Description of the Prior Art There are many applications for two stage servo valves of the type which employ an electric actuator to control a first hydraulic regulating device which, in turn, effects the displacement of the slide of the main valve distributor of a second hydraulic stage. It is, of course, desirable that such devices should utilize a constant pressure source and an electric driving voltage. Use of a two stage hydraulic system is dictated by the fact that the electric torque motors generally employed for such servomechanisms do not have sufficient power to operate the main valve distributor.

As noted, two stage hydraulic servomechanisms are known in the art. In the prior art devices, the first stage consists of a regulating device with a continuous leakage type output. Thus, a typical first stage may comprise a calibrated leakage port which is .throttled via a butterfly valve or equivalent device operated by the electric torque motor. In these prior art devices, servo-positioning of the slideof the main or second stage valve distributor has been achieved either through the use of a differential lever connected to the first stage or with the aid of powerful return springs associated with the slide of the main valve distributor. As is well known, employment of springs results inmodification of the transfer function by introducing a term denoting slide position.

SUMMARY OF THE INVENTION The present invention overcomes the abovediscussed and other disadvantages of the prior art by providing a novel and improved electro-hydraulic two stage servo'mechanism. In. accordancewith the invention, the first hydraulic stage comprises a device without permanent leakage and, in particular, a servo control valve employing a standard slide. Also in accordance with the invention, closed loop control is obtained solely by hydraulic means without the employment of either springs or differential levers. In achieving this control, the invention also comprises a second stage servo valve; the second distributor employing a floating slide which is operated exclusively by an applied pressure differential.

In a preferred embodiment of the present invention, the two hydraulic servo valves or distributors, while mechanically independent of one another, are ranged so as to be coaxial with one another. Also in accordance with a preferred embodiment of the invention, the two stage hydraulic distribution device and the electrical actuator comprise two separate subassemblies. The transmission of control movements from the electric actuator to the hydraulic assembly is affected by a linkage comprising at least one horizontal shaft which is provided with suitable sealing means whereby leakage of operating fluid from the hydraulic assembly is minimized.

2 BRIEF DESCRIPTION OF THE DRAWING DESCRIPTION OF THE PREFERRED EMBODIMENT With referencejnow to FIG. 1, the block or casing of the hydraulic distributor section of the present invention is indicated-at 1 and the housing or block for the electrical actuator is indicated at 2. In the interest of clarity, the casings for the electrical and hydraulic cylinders have been'depicted with broken lines. The output shaft of the electric motor is connected to a sleeve 3 of the valve distributor of the first hydraulic stage via a linkage comprising members 4, 5 and 6. Linkage member 6 is in turn'connected via a horizontal shaft 8 to an arm 7. The arm 7 is connected by a horizontal pin 9 to distributor sleeve 3; pin 9 passing through a hole or aperture in the sleeve. In order to prevent leakage of operating fluid through the walls of casing of hydraulic distribution block 1, suitable sealing means 10 are provided about the horizontal shaft-8 where it passes through thewall of casing l. I

Referring now to FIG. 2, the casing 2 which receives and supports the electric torque motor has been represented symbolically by'a rectangle and, in the interest of clarity, the relative positioning of the electrical and hydraulic su'bassemblies has been changed from that shown in FIG. 1. Considering the hydraulic subassembly,which has'beenshown in section, the valve or distributor comprising the first hydraulic stage is indicated at 12 and the valve or distributor comprising the second hydraulic stage is indicated at 25. Pressurized operating fluid from a constant pressure source, not shown, is delivered to casing 1 via passage. 14. The load on the servomechanism is connected to outlet passages 15 and 16 in casing l and thus the operating fluid leaves the casing -via passages 15 and 16' when transmitted to the point of utilization. Passage [7 in casing l is connected to a reservoir, not shown.

The slides of both distributors or hydraulic stages are shown in FIG. 2 in their middle position. Oil or other operating fluid at pressure 'P will be delivered, via passage 18 and other conduits in casing 1, ma pressure relief valve 20 of any conventional type. Relief valve 20 has, of course, been illustratedschematically in FIG. 2.

The pressure at the outlet of relief valve 20, and upstream of a filter 2l, will be at pressure P as shown. Any fluid leaking from relief valve 20 will be returned to the reservoir via conduits 22 and 23 and passage 17. The pressure P, is transmitted via conduit 24 to a first end of the chamber of the second stage hydraulic distributor 25 and-thus will act on the right hand end of slide 13 of distributor 25. Pressure P,-will also be transmittedtothe chamber of the first stage hydraulicdistributor via conduit 26.

The slides of the first and second stage hydraulic distributors are, in the disclosed preferred embodiment, arranged coaxially. The slide member of first stage distributor 12 is integral with the above-discussed sleeve 3. The distributor 12, which is housed in a piston 27, is a four-way distributor. The input 28 to distributor 12 is in communication with the conduit 26 while a pair of return passages 29 and 30 are in communication with the reservoir via passage .17. Distributor 12 also includes a passage 31 which communicates with thechamber 33 at the left hand end of piston 27.

The piston 27 moves in'a jacket 32 which is coaxial with the distributors 12 and 25. In the disclosed embodiment the-piston has been shown as distinct and separate element from the slide 13 of distributor 25. However, it is to be noted that piston 27 and slide 13 may be integral. The surface area of the left end of piston 27 is, in a preferred embodiment, equal to twice the surface area of the right hand end of the slide 13 of distributor 25. v r

As indicated in FIG. 2, a pressure P will be created in chamber 33 at the leftend of piston 27. With the hydraulic systemin a state of equilibrium, the pressure l will beone-half of the pressure P, as aresult of the inherent leakages'in the system which are necessary to permit thefre'e movement of the slides in their respective chambers. In practice, the valves of these leakages are between 50 and 200 CC per'minute. This amount of leakage is, .of course, considerably below the permanent leakage allowed by the devices whose functioning depends specifically on the existence of a permanent leakage.

When the electrical actuator displaces the sleeve 3 and hence the slide of the distributor 12 towards the left, as'shown in FIG. 2, the chamber 33 is connected .with the return to the reservoir via passage 31, passage 30 and chamber 34. As a result of the connection of the chamber 33 to the reservoir, the slide 13 of distributor 25 will move to the left under the influence of pressure P Thus, the pressure inlet 14 will be brought into direct communication with the outlet passage 15.

if, on thegother hand, the electrical actuator or torque motor'causes sleeve 3 to be displaced to the right, the chamber 33 is brought into communication with the pressure P, inlet and the piston 27 will move .to the right as shown in FIG. 2. Movement of piston 27 to the right entrains the slide of distributor 25 and movement of the slide results in establishment of communication between inlet passage 14 and outlet 16. Thus, through the application of very slight force on the sleeve 3, the slide of distributor 25 may be moved in either of two opposite directions and movements of this slide will faithfully follow the movements of the actuator with a static precision approaching 1 micron, dynamically up to 60 H,', for example, with negligible dephasing.

'It may be seen by way of comparison with existing two stage servo valves which operate by means of an output regulating device, the valves according to the present invention do not employ a calibrated port of small diameter and therefore are much less susceptible to the effects of impurities. In this respect, it is possible to employ a protective valve with a filtering capacity of 30 microns whereas the filters in the prior art have had to have a capacity of at least l microns. Further, in ac- 'cluding:

cordance with the present invention,- the valves have no elastic elements which are subject to fatigue and thus are extremely strong and reliable.

As noted above, the main slide 13 of the present in- 5 vention faithfully follows movements of the torque 15 special expedience such as internal leakages, friction,

or'pressure feedback.

As noted above,- the present invention reduces the permanent or steady state consumption of operating fluid to operational leakages. Further, the present invention permits absolute separation of the electric torque motor from the distribution of the operating fluid thereby preventing any breakdown of theelectric- 25 around the magnetic parts of the electrical actuator. I

The axial freedom of the slide of distributor 12 in piston 27 is reduced to a few tenths of a millimeter whereas the stroke of the main slide 13 is several millimeters. Thus, under the influence of the electric control signal delivered to the torque motor, the assembly of the piston 27 and the slide of distributor 25 is placed in a functional position before any pressure is exerted.

While a preferred embodiment has been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the present invention. Accordingly, it is to be understood that the present invention has been described by way of illustration and notlimitationf What is claimed is:

1. An electro-hydraulicservomechanism comprising:

electrical actuator means; a

two-stage fluid regulator means for'controlling the pressure applied to a load, said regulator means ina first hydraulic stage including a distributor valve, said first stage,valve having a slide member; and a second hydraulic stage including a distributor valve, said second stage valve having a floating slide member and defining an inlet for a source of pressurized fluid and at least two outlets for said fluid, said second stage valveslide havinga first reaction surface of smaller area than a first surface of said first stage valve slide, said first and second stage valve slide members cooperatmeans coupling movements of said electrical actuator means to the first stage of said regulator means. 2. The'apparatus of claim 1 wherein the slides of said first and second stage valves are coaxial.

3. The apparatus of claim ,1 wherein said first. and second stage valves define a closed loop control valve.

4. The apparatus of claim 1 wherein said valve slides are coaxial and mechanically independent.

5. The apparatus of claim 1 wherein said actuator and regulator are positioned in separate housings and wherein said coupling means comprises:

means mechanically connecting the output shaft of said actuator to the slide of said first stage valve, said connecting means including a shaft whichpasses into said regulator housing, said shaft being provided with sealing means whereby undesired leakage of operating fluid from said regulator housing is prevented.

6. A two-stage hydraulic distributor device comprisa power circuit, said power circuit including:

a valve housing, said housing defining a bore, said housing being provided with an inlet port through which pressurized fluid may be delivered to said bore and an exhaust port, said housing further being provided with at least a pair of outlet ports adapted for connection to a fluid utilizing load; and

power distribution valve means disposed in said housing bore, said power distribution valve means including a longitudinally movablefloating power valve member for controlling distribution of fluid between said inlet port and respective of said outlet ports; and

a control circuit, said control circuit including:

floating piston means disposed in said valve housing bore, said floating piston means being provided with a bore and being disposed in pushing relationship with said floating power valve member in at least one direction of movement; pilot valve means disposed at least in part in said floating piston means bore, said pilot valve means including a longitudinally movable valve member, said pilot valve means controlling the application of control pressure to a first end of said floating piston means; and means connected to said pilot valve means and responsive to an input signal for positioning said pilot valve movable member. 7. The apparatus of claim 6 wherein said floating powervalve member is integral with said floating piston means.

8. The apparatus of claim 6 wherein said distribution device further comprises:

means for coupling said housing inlet port to said pilot valve means and to a first end of said longitudinaliy movable power valve member which is not coupled to said floating piston means, said coupling means developing a control pressure. 9. The apparatus of claim 6 wherein said valve members and piston are coaxial with-one another.

10. The apparatus of claim 8 wherein said valve members and piston are coaxial with one another. 

1. An electro-hydraulic servomechanism comprising: electrical actuator means; two-stage fluid regulator means for controlling the pressure applied to a load, said regulator means including: a first hydraulic stage including a distributor valve, said first stage valve having a slide member; and a second hydraulic stage including a distributor valve, said second stage valve having a floating slide member and defining an inlet for a source of pressurized fluid and at least two outlets for said fluid, said second stage valve slide having a first reaction surface of smaller area than a first surface of said first stage valve slide, said first and second stage valve slide members cooperating to define a differential area piston having an intermediate equilibrium position; means delivering fluid under pressure to said first and second stage valves; and means coupling movements of said electrical actuator means to the first stage of said regulator means.
 2. The apparatus of claim 1 wherein the slides of said first and second stage valves are coaxial.
 3. The apparatus of claim 1 wherein said first and second stage valves define a closed loop control valve.
 4. The apparatus of claim 1 wherein said valve slides are coaxial and mechanically independent.
 5. The apparatus of claim 1 wherein said actuator and regulator are positioned in separate housings and wherein said coupling means comprises: means mechanically connecting the output shaft of said actuator to the slide of said first stage valve, said connecting means including a shaft which passes into said regulator housing, said shaft being provided with sealing means whereby undesired leakage of operating fluid from said regulator housing is prevented.
 6. A two-stage hydraulic distributor device comprising: a power circuit, said power circuit including: a valve housing, said housing defining a bore, said housing being provided with an inlet port through which pressurized fluid may be delivered to said bore and an exhaust port, said housing further being provided with at least a pair of outlet ports adapted for connection to a fluid utilizing load; and power distribution valve means disposed in said housing bore, said power distribution valve means including a longitudinally movable floating power valve member for controlling distribution of fluid between said inlet port and respective of said outlet ports; and a control circuit, said control circuit including: floating piston means disposed in said valve housing bore, said floating piston means being provided with a bore and being disposed in pushing relationship with said floating power valve member in at least one direction of movement; pilot valve means disposed at least in part in said floating piston means bore, said pilot valve means including a lonGitudinally movable valve member, said pilot valve means controlling the application of control pressure to a first end of said floating piston means; and means connected to said pilot valve means and responsive to an input signal for positioning said pilot valve movable member.
 7. The apparatus of claim 6 wherein said floating power valve member is integral with said floating piston means.
 8. The apparatus of claim 6 wherein said distribution device further comprises: means for coupling said housing inlet port to said pilot valve means and to a first end of said longitudinally movable power valve member which is not coupled to said floating piston means, said coupling means developing a control pressure.
 9. The apparatus of claim 6 wherein said valve members and piston are coaxial with one another.
 10. The apparatus of claim 8 wherein said valve members and piston are coaxial with one another. 